JPS58217475A - Method of directly bonding metal piece to oxide ceramic substrate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves heating an oxide ceramic substrate covered with metal pieces in an oxygen-containing atmosphere to the eutectic point of the metal and oxide, but below the melting point of the metal. This invention relates to a method for directly bonding a metal piece with a metal oxide layer to an oxide ceramic or substrate.

The above method is known from DE 2508224 A1. In this method, pre-oxidized metal is used in order to enable adhesion everywhere between metal and ceramic, even in the case of large area bonds. Also, the metal piece is bent in advance so that it gradually comes into contact with the ceramic substrate when heated. In this way, air bubbles that form between the metal and ceramic are pushed out.

However, this method is expensive and complicated. Also, if the metal strip or the ceramic substrate is preformed in a complicated manner, a bending of the metal strip is no longer possible or the metal strip does not contact the substrate sufficiently uniformly. However, when using a reactive atmosphere consisting of about 0.01 to 0.5 volumes of oxygen (with a small amount of nitrogen), the exposed surfaces of the metal are covered with an oxide layer, which is later removed again. Must.

A method is described in DE-A-2633869 in which a metal foil, preferably a copper foil, is first immersed in an acid and then the metal foil with an oxide layer is brought into contact with an oxide ceramic substrate, preferably oxidized and made of aluminum or beryllium oxide. It is well known by the number. According to this method, the metal foil and the substrate are heated in an inert atmosphere at a temperature between the eutectic point of the copper and copper oxide and the melting point of the copper until a hypoeutectic melt of the copper and the substrate is formed. If a certain minimum oxygen partial pressure is not maintained in the surrounding atmosphere, CuO will be reduced to CO at supported processing temperatures.
Heating in an inert atmosphere does not result in the desired strong adhesive bond between the copper and the ceramic, since the copper is reduced to 20 and the Cu 20 to ICU. Reduced copper is not combined with Senmix.

Furthermore, DE 26 33 869 A1 proposes the use of an oxygen-containing copper material without an oxide coating in place of pre-oxidized copper. In this case as well, if the minimum oxygen partial pressure is not maintained in the furnace atmosphere, there will be no bond between the copper and the ceramic, and the oxygen dissolved in the copper will diffuse to the contact surface between the copper and the ceramic. enclosed,
Experiments have shown that as a result, bubbles are generated, leading to defects in the metal-ceramic bond.

Another method for bonding metal and non-metallic substrates has been published in West Germany, which differs from the previously described method in that bare metal foils, especially copper foils, without pre-oxidation, are bonded to oxide ceramics in a reactive, especially oxygen-containing atmosphere. Patent Publication No. 2319854 discloses a method for reducing thirst. In this method, before the original bonding process takes place,
Oxygen in the atmosphere must first oxidize the surface of the copper. However, especially if the area of the bond between the ceramic and the copper is large, a sufficient amount of oxygen cannot enter the gap between the ceramic and the copper, so that bubble-like unattached spots occur. Also 0, 01 to 0.5
At the aforementioned oxygen amount of 1 volume, the side of the copper foil facing away from the ceramic substrate is covered with a thick black copper oxide layer. This oxidized steel layer has to be removed again in an auxiliary step, especially before reprocessing in the semiconductor industry. Amounts of oxygen less than 0.01 volumetric drops are clearly undesirable. This is because no bond occurs between the copper and the ceramic in that case.

A method for directly bonding copper and ceramics is also known from British Patent Publication No. 761045. A number of process variants are described therein in which the furnace atmosphere is at least temporarily at an oxidizing pressure and at least temporarily at a reducing pressure. Vacuum heating is also suggested. Common to all process variants is that the bonding of copper and ceramic takes place in the temperature range from 1083° C. to 1235° C., ie above the melting point of copper and below the melting point of copper oxide. In that case, the formation of a temperature-thick oxide layer on the exposed surfaces of the copper is prevented by masking with a protective material such as aluminum oxide or silver. However, the covering and subsequent removal of the protective material requires auxiliary steps. Another drawback is that the required temperature range is extremely narrow.

It is an object of the present invention to provide a method for direct bonding of a metal piece and an oxide-ceramic substrate, in which an oxide-free metal surface is easily obtained, as well as a complete, bubble-free bond between the metal piece and the ceramic substrate. The purpose is to provide an improved method.

This object is achieved by the features indicated in claim 1.

The advantage obtained by the invention is, inter alia, that by suitable treatment operations, "oxide-free metal surfaces can be obtained without a subsequent reduction step."

Moreover, the method is suitable for economical mass production.

``No additional processing is required for reprocessing the metal-ceramic bonded system taken out of the continuous furnace.

A preferred embodiment of the invention is as shown in the dependent frame.

Next, the present invention will be explained in detail based on examples.

Before carrying out the actual method, the metal cantilever is provided with an oxide layer on the copper plate. The thickness of the oxide should correspond to approximately one tenth of the surface roughness of the ceramic substrate used, for example aluminum oxide ceramics. Preferably, the oxidation is carried out chemically. The copper plate can be oxidized on one or both sides, and the oxidized side is placed flat on top of the ceramic substrate. Copper plates can be provided on both sides of the ceramic substrate to compensate for curvature curvature due to thermal stress due to the difference in thermal expansion of copper and ceramics.

The copper plate is preferably made of oxygen-free copper and must be flat. There should also be no cracks on the cut edges. Otherwise, there will not be a sufficiently intimate contact between the oxidized copper plate and the ceramic substrate.

As shown in FIG. 1, a substrate 2 with a copper plate 1 is placed on a base plate 3, preferably consisting of a silicon carbide or pyrolead core and a silicon carbide coating. The bed plate 3 is placed on the chain conveyor 4 of the continuous furnace 5.

The continuous furnace 5 has a tunnel (metal cylinder) 6 that is open on both sides. There are five spatially divided temperature zones within the tunnel 6.

The heating zone l at the entrance of the channel and the three heating zones n at the center.
, m, ① and a cooling zone V at the exit portion appears. tunnel 6
The two open ends of are provided with movably mounted, non-tight metal fittings 7,8. The central part of the tunnel 6 is surrounded by three heating elements 9 * 10 t 11 creating heating zones n, m, tv.

At its outer end, the tunnel has a cooling body 12 surrounding its bulkhead. The temperature inside the tunnel, which is kept constant by the three heating elements xo and 11m12, can be set independently of each other and adjusted with an accuracy of 1 to 2 degrees.

The tunnel 6 also has gas inlet connecting pipes 13 and 14 at both ends. A further gas inlet connecting pipe 15,16 connects the first heating element 9
or behind the third heating element 11. The gas inlet connecting pipe 15 is bifurcated and is connected to two gas supply pipes.

For precise adjustment of gas flow rate, gas inlet connecting pipe 13.
A flow meter 17.20.21 is provided at 16.14. Another flow meter 1B, 19- is located on the way from the two gas supply pipes to the gas inlet connecting pipe 15. These two gas supply pipes are equipped with an auxiliary regulating valve 2 for precise regulation of a given flow rate.
It has 2°23. The above-mentioned regulating valve 24 is also provided in the I gas inlet connecting pipe 16.

The endless chain conveyor of continuous furnace 5 is Row 22
5 and 26. The base plate 3 placed on the chain 4 in front of the tunnel entrance passes through the opening baffle 7 and reaches the temperature rising zone l at the entrance portion inside the tunnel. /4
Nitrogen is blown in via a gas inlet connecting pipe 13 arranged in the tunnel behind the tube 7. This nitrogen forms a gas jacket and prevents oxygen-rich outside air (up to 5% upon opening of the baffle 7) from penetrating inside the tunnel.

A substrate 2 covered with a copper plate 1 is placed on a base plate 3 and passes through a temperature increasing zone (2) and a heating zone (2) in about 20 minutes. The temperature in the central section of the heating zone (2) is adjusted to approximately 960°C. When entering the central section of the heating zone ■, the parts to be joined meet the eutectic point of copper and copper oxide (1
065° C.) and the melting point of copper (1083° C.), preferably a maximum temperature of 1070° C. to 1072° C., a eutectic melt is formed between the copper plate 1 and the ceramic substrate 2.

The copper-clad substrate remains in this high temperature reaction zone for about 1 to 2 minutes during passage. A nitrogen atmosphere containing oxygen at 20 to 50 vpm dominates the temperature increasing zone I and heating zones (1) and (2) inside the tunnel. In order to maintain this atmosphere, a defined nitrogen/oxygen mixture is continuously blown in via the gas inlet connecting pipe 15, with a flow meter 19-regulating valve 23 for the oxygen supply and a flow meter 19 for the nitrogen supply. 18 - A regulating valve 22 is provided.

The mixture is evenly distributed by turbulent flow into the multi-zones 1, If and III and exits the tunnel 6 via the baffle '7.

After the bonding process, that is, the solidification of the eutectic melt, the base plate 3 passing on the chain 4 reaches the heating zone of the tunnel 6.
From then on, it enters the heating zone■. Is it already about 960℃ in the central section of the gold ceramic composite yarn L1 heating unit? V has been rejected. The metal-ceramic composite system is cooled in the heating zone (■) and the subsequent original cooling zone (■) in a pure nitrogen atmosphere. When using a copper plate 1 with oxidized surfaces on both sides, the copper-removed surface is reduced. The nitrogen atmosphere is obtained by blowing pure nitrogen into the tunnel interior through the gas inlet connecting pipe 16. The nitrogen is evenly distributed by turbulent flow into the sections (1) and (V) and exits the tunnel (6) via the baffle (8).

Due to the special nozzle arrangement or nozzle shape of the gas inlet connecting pipes 15 and 16, and by appropriate adjustment of the flow rates through the two inlet connecting pipes, the nitrogen/oxygen atmosphere in the zone 11n1■ and the zones ■, ■ auxiliary gas inside the tunnel during a pure nitrogen atmosphere.

Relatively clear boundaries can be obtained without full.

The entire kinetic process lasts approximately 20 minutes. To facilitate cooling of the metal-ceramic composite system, a cooling body 12, for example water-cooled, is used at the end of the tunnel.

Via the gas inlet connecting pipe 14, polynitrogen is also blown in to form a gas jacket, which prevents outside air from entering the inside of the tunnel (particularly when the baffle 8 is opened). Upon exiting the continuous furnace 5 through the baffle 8, the metal-ceramic composite system has been cooled to room temperature. Copper surfaces tend to have a metallic luster and virtually never reoxidize. Since the amount of oxide generated is very small, it can be easily removed by a conventional 7 lux during subsequent soldering operations. Since the adhesion of copper to the ceramic is very good, with almost no bubbles, part of the ceramic is torn off along with the copper in the peel test.

Figure 2 shows the temperature gradients that appear in each zone of the continuous furnace. In that case, the temperature axis T shows only an upper temperature range of approximately 960°C to 1072°C. In particular, it is clear from Figure 2 that the temperature gradient rises or falls rapidly in the heating zones ①, ②, and ②.

The temperature range of 1065° C. or higher, which is necessary for the formation of a eutectic melt, is reached in the central section of the heating zone (1).

The drop on both sides of the temperature gradient from the maximum temperature of 1072° C. to the predetermined temperature T=960° C. in the middle of heating zones ① and ② is rapid. In other words, the temperature rise and cooling of the metal-ceramic composite system occurs extremely rapidly in the temperature range from 960°C to 1072°C. This treatment operation (and the combination of the nitrogen-oxygen atmosphere described above) particularly results in a nearly bubble-free metal-ceramic composite system with a shiny metallic surface.

[Brief explanation of the drawing]

Figure 1 is a structural diagram of a continuous furnace suitable for implementing this method;
The figure shows a diagram of the temperature gradient in a continuous furnace. DESCRIPTION OF SYMBOLS 1... Metal piece-copper plate, 2... Paramic substrate on saponified material, 6... Continuous furnace, 6... Tunnel, 9.10°J J, 12... Heating element, 15.16 ...Inlet connecting pipe, 17 * 18 e 1 b e 2 (7 *
21...Flowmeter, 22...Control valve. Applicant's representative Patent attorney Takehiko Suzue [-- Page 1: (Contents A: No changes) Fig, 1 To Takuta Continued from page 1 0 Inventor Helmut Kaeser Zeher, Switzerland - 5242 Biel-Hinterhofstrasse 82 Procedural amendment (method) % formula % 1. Indication of the case Patent application No. 16301/1982 2° Invention 9J Name Method of directly bonding a metal piece and an oxide ceramic substrate 3, Amendment Relationship with the case of patent applicant Pura Kun and Paris Kun and C. Akchengsellschaft 4, agent May 31, 1980 6 Subject of amendment

Claims (1)

[Claims] 1) Metal oxide is formed on the surface by heating an oxide ceramic substrate covered with metal pieces in an oxygen-containing atmosphere to the eutectic point of the metal and oxide, but below the melting point of the metal. In the method of directly bonding the layer-attaching metal piece to the oxide ceramic substrate, heating is carried out in a continuous furnace in an oxygen-containing atmosphere with addition of 20 to 50 vpm of oxygen, and solidification of the eutectic melt is carried out in a pure nitrogen atmosphere. After that, the method is characterized by cooling in a continuous furnace. 2) The method according to claim 1, characterized in that both heating and cooling of the members to be joined are carried out rapidly in an upper temperature range. 3) The method according to claim 1 or 2, characterized in that a copper plate is used as the metal piece. 4) A method according to any one of claims 1 to 3, characterized in that aluminum oxide is used as the oxide ceramic substrate.